1. Field of the Invention
The present invention relates to a polymer scale preventive agent useful in polymerization of a monomer having an ethylenically unsaturated double bond, a polymerization vessel effective in preventing polymer scale deposition, and a process of producing a polymer using said vessel. 2. Description of the Prior Art
In processes of preparing polymers by polymerizing a monomer in a polymerization vessel, the problem that polymer deposits on the inner wall surfaces and so forth in the form of scale, is known. The deposition of the polymer scale on the inner wall results in disadvantages that the yield of the polymer and cooling capacity of the polymerization vessel are lowered; that the polymer scale may peel and mix into a polymeric product, thereby impairing the quality of the polymeric product; and that removal of such polymer scale is laborious and hence time-consuming. Further, since the polymer scale contains unreacted monomers and operators may be exposed thereto, which may cause physical disorders in the operators.
Heretofore, as methods for preventing polymer scale deposition on the inner wall surface and so forth of a polymerization vessel in polymerization of a monomer having an ethylenically unsaturated double bond, methods in which substances exemplified below are coated on the inner wall surface, etc. as a scale preventive agent, have been known.
For example, particular polar organic compounds (Japanese Patent Publication (KOKOKU) No. 45-30343(1970)), a dye or pigment (Japanese Patent Publication (KOKOKU) Nos. 45-30835(1970) and 52-24953(1977)), an aromatic amine compound (Japanese Pre-examination Patent Publication (KOKAI) No. 51-50887(1976) and a reaction product of a phenolic compound and an aromatic aldehyde (Japanese Pre-examination Patent publication (KOKAI) No. 55-54317(1980)) are disclosed.
The scale preventive agents containing the polar organic compounds described in Japanese Patent Publication (KOKOKU) No. 45-30343(1960), the dyes or pigments described in Japanese Patent Publication (KOKOKU) Nos. 45-30835(1960) and 52-24953(1977) are effective in the polymerization of vinyl halides such as vinyl chloride or monomeric mixture containing a vinyl halide as a major component and a small amount of monomers copolymerizable therewith; however, it is difficult to effectively prevent the deposition of polymer scale in the polymerization of vinyl acetate, acrylates, acrylonitrile, styrene, .alpha.-methylstyrene or like monomers because these show a strong dissolving action against the coatings formed from the scale preventive agents above.
In the meantime, vinyl chloride polymers obtained by polymerization are required to have a good witness. That is, when polymeric products such as vinyl chloride polymers are formed or molded with no addition of a coloring agent, the resulting formed or molded product is colored more or less. This coloration is called initial coloration, which is required to be as low as possible.
However, in the case where vinyl chloride or the like is suspension polymerized in a polymerization vessel in which a polymer scale preventive agent comprising the substances mentioned above has been coated, polymeric products obtained are more or less colored and their quality is low. Presumably, the coloration is due to the fact that most of the conventional polymer scale preventive agents are colored. That is, presumably, when polymerization is conducted in a polymerization vessel having the coating mentioned above, the coating is dissolved or peeled into the polymerization mass, causing the coloration of polymeric products.